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Lee, Sooheyong,Jo, Wonhyuk,Wi, Haeng Sub,Gutt, C,Lee, Geun Woo Optical Society of America 2014 Optics express Vol.22 No.18
<P>We report an alternate light scattering approach to measure intermediate scattering function and structures of colloidal suspension by using two-pulse speckle contrast correlation analysis. By systematically controlling time-delays between two laser pulses incident on the sample, we are able to monitor transient evolution of coherent diffraction pattern, from which particle dynamics at different length and time scales are obtained simultaneously. Our result demonstrates the feasibility of utilizing a megapixel detector to achieve sufficient data statistics in a short amount of time while enabling microsecond time-resolution. Ultimately, this method provides means to measure high-speed dynamics well beyond the time response limit of a large area two-dimensional (2D) detector.</P>
Lee, Sooheyong,Wi, Haeng Sub,Jo, Wonhyuk,Cho, Yong Chan,Lee, Hyun Hwi,Jeong, Se-Young,Kim, Yong-Il,Lee, Geun Woo National Academy of Sciences 2016 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.113 No.48
<P>Solution studies have proposed that crystal nucleation can take more complex pathways than previously expected in classical nucleation theory, such as formation of prenucleation clusters or densified amorphous/liquid phases. These findings show that it is possible to separate fluctuations in the different order parameters governing crystal nucleation, that is, density and structure. However, a direct observation of the multipathways from aqueous solutions remains a great challenge because heterogeneous nucleation sites, such as container walls, can prevent these paths. Here, we demonstrate the existence of multiple pathways of nucleation in highly supersaturated aqueous KH2PO4 (KDP) solution using the combination of a containerless device (electrostatic levitation), and in situ micro-Raman and synchrotron X-ray scattering. Specifically, we find that, at an unprecedentedly deep level of supersaturation, a high-concentration KDP solution first transforms into a metastable crystal before reaching stability at room temperature. However, a low-concentration solution, with different local structures, directly transforms into the stable crystal phase. These apparent multiple pathways of crystallization depend on the degree of supersaturation.</P>
In-situ synthesis of TiC/Fe alloy composites with high strength and hardness by reactive sintering
Lee, Junho,Lee, Dongju,Song, Myung Hoon,Rhee, Wonhyuk,Ryu, Ho Jin,Hong, Soon Hyung Elsevier 2018 Journal of materials science & technology Vol.34 No.8
<P><B>Abstract</B></P> <P>Fe alloy composites reinforced with in-situ titanium carbide (TiC) particles were fabricated by reactive sintering using different reactant C/Ti ratios of 0.8, 0.9, 1 and 1.1 to investigate the microstructure and mechanical properties of in-situ TiC/Fe alloy composites. The microstructure showed that the in-situ synthesized TiC particles were spherical with a size of 1–3μm, irrespective of C/Ti ratio. The stoichiometry of in-situ TiC increased from 0.85 to 0.88 with increasing C/Ti ratio from 0.8 to 0.9, but remained almost unchanged for C/Ti ratios between 0.9 and 1.1 due to the same driving force for carbon diffusion in TiC<I> <SUB>x</SUB> </I> at the common sintering temperature. The in-situ TiC/Fe alloy composite with C/Ti=0.9 showed improved mechanical properties compared with other C/Ti ratios because the presence of excess carbon (C/Ti=1 and 1.1) resulted in unreacted carbon within the Fe alloy matrix, while insufficient carbon (C/Ti=0.8) caused the depletion of carbon from the Fe alloy matrix, leading to a significant decrease in hardness. This study presents that the maximized hardness and superior strength of in-situ TiC/Fe alloy composites can be achieved by microstructure control and stoichiometric analysis of the in-situ synthesized TiC particles, while maintaining the ductility of the composites, compared to those of the unreinforced Fe alloy. Therefore, we anticipate that the in-situ synthesized TiC/Fe alloy composites with enhanced mechanical properties have great potential in cutting tool, mold and roller material applications.</P>
Delayed auger recombination in silicon measured by time-resolved X-ray scattering
Jo, Wonhyuk,Landahl, Eric C.,Kim, Seongheun,Lee, Dong Ryeol,Lee, Sooheyong ELSEVIER 2018 CURRENT APPLIED PHYSICS Vol.18 No.11
<P>We report a new method of measuring the non-radiative recombination rate in bulk Silicon. Synchrotron time-resolved x-ray scattering (TRXS) combines femtometer spatial sensitivity with nanosecond time resolution to record the temporal evolution of a crystal lattice following intense ultrafast laser excitation. Modeling this data requires an Auger recombination time that is considerably slower than previous measurements, which were made at lower laser intensifies while probing only a relatively shallow surface depth. We attribute this difference to an enhanced Coulomb interaction that has been predicted to occur in bulk materials with high densities of photoexcited charge carriers.</P>
최원혁(Wonhyuk Choi),이동길(DongGill Lee),이시영(Si-Young Lee),김승호(Sung-Ho Kim) 한국정보과학회 2001 정보과학회논문지 : 소프트웨어 및 응용 Vol.28 No.4
본 논문에서는 교환기와 같은 실시간 분산 시스템의 개발을 위한 SDL과 CHILL에 기반한 통합 소프트웨어 개발 방법이 제시된다. 이미 다양한 분야에서 SDL과 CHILL의 도구들이 각각 개발되어 왔지만, 본 논문에서는 이들을 통합할 수 있도록 SDL에서 CHILL로의 자동 코드 생성과 심벌 디버깅 환경에 중점을 둔다. 이는 완벽한 수행과 심벌 추적 정보의 삽입을 위한 자동 코드 생성 단계와 SDL 심벌 디버거와 CHILL 시험 환경을 이용한 실시간 심벌 디버깅 단계로 이루어지며, 첫째 SDL에 기반한 정형명세, 둘째 설계의 검증과 확인, 셋째 자동 코드 생성, 넷째 분산된 실시간 병행 CHILL 프로그램의 디버깅, 그리고 마지막으로 응용 프로그램의 CHILL에 기반한 호스트 통합 시험을 제공한다. In this paper, we present an integrated software developing method for real-time distributed system like switching system based on SDL and CHILL. As many SDL and CHILL tools are already developed in various application areas, we concentrate on automatic code generation from SDL to CHILL and symbolic debugging environment to integrate them : automatic code generation step for complete execution and insertion of symbolic tracing information, and run-time symbolic debugging step using SDL symbol debugger and testing environment for CHILL. Our approach can provide 1) formal specification based on SDL, 2) verification and validation of the design, 2) automatic code generation, 4) debugging of distributed real-time concurrent CHILL program, 5) simulation of application software for integrated testing on the host machine based on CHILL.